1. Field of the Invention
The present invention relates generally to a wireless power transmission system, and more particularly, to a method of controlling power transmission in a power transmitter against overvoltage at a power receiver.
2. Description of the Related Art
Wireless charging technology, or contactless charging technology, has recently been developed and applied to many different electronic devices. The wireless charging technology, using wireless power transmission and reception, enables, for example, a battery of a cell phone to be automatically charged by placing the cell phone on a charging pad, without requiring a separate charging connector. The wireless charging technology wirelessly charges electronic products and eliminates the need for a wired charger, thus contributing to waterproofing and portability of the electronic products.
In a resonance-based charging method, when a power receiver, requiring charging, is located in a power transmission area of a power transmitter for transmitting wireless power, the power transmitter may charge the power receiver. When the power receiver provides power information for the power transmitter, the power transmitter transmits the power demanded by the power receiver, to the power receiver. The power receiver starts charging only after receiving a start charging command.
As described above, after receiving the start charging command, the power receiver starts charging, e.g., by controlling a switch to be connected to the charger (or battery). However, since the power transmitter transmits power immediately after completing preparations of the power transmission, voltage that is input to the power receiver may increase to overvoltage, which may damage the circuit on the power transmission line at the power receiver.
Furthermore, when another power receiver is already performing charging in the charging area, the transmission power of the power transmitter for the other power receiver may decrease to a point where charging of the other power receiver might be stopped.